Polymerization of cyclic esters



Amer. Ber. 36, 1200 (1903).

United States Patent 3,021,316 PQLYMERIZATION OF CYCLIC ESTERS Eugene F. Cox and Fritz Hostettler, Charleston, W. Va.,

assrgnors to Union Carbide Corporation, a corporation of New York No Drawing. Filed Dec. 3, 1959, Ser. No. 856,911 30 Claims. (Cl. 26078.3)

This invention relates to a process for polymerizing cyclic esters and to the products resulting therefrom. The most generally familiar works on the polymerlzation of lactones are the now classical investigations of W. H. Carothers. For instance, Carothers was able to polymerize delta-valerolactone to poly-delta-valerolactone by heating at 8085 C. for a period of about 13 days, or by contacting delta-valerolactone with potassrum carbonate catalyst at a temperature of 8085 C. for a period of about days. The resulting polymers were soft waxes possessing average molecular weights of approximately 2000 which had relatively low thermal stabilities. The literature reports that attempts to polymerize gamma-butyrolactone have been unsuccessful, and the corresponding polyester is not known. In 1934, there was reported the preparation of polyepsilon-caprolactone by heating epsilon-caprolactone at about 150 C. for a period of 12 hours, or by contacting epsilon-caprolactone with potassium carbonate at about 150 C. for a period of 5 hours. The resulting epsiloncaprolactone polymers had melting points of about 53- 55 C. and average molecular weights of about 4000. The polymers were hard, brittle waxes which could not be cold-drawn into fibers. Bischoif and Waldon describe the transformation of glycolide under the influence of heat or a trace of zinc chloride into a polymeric solid melting at 220 C. On being distilled in a vacuum it was reconverted to the monomer melting at 86-87 C. The literature also reports the polymerization of lactide at elevated temperatures to a resinous mass. A similar effect is also obtained at relatively lower temperatures by employing potassium carbonate as the catayst.

In a broad aspect the present invention is directed to the process for polymerizing monomeric cyclic esters in contact with certain metal hydride catalysts to produce useful polyester products, both the cyclic ester reagents and the metal hydride catalysts being described hereinafter in a more appropriate section. The average molecular weights of the resulting polymers can range from about several hundred to about several thousand. The 'homopolymers, copolymers, and terpolymers prepared by the practice of the instant invention are highly useful products as will become apparent at a later section herein. In addition, the polymerization reaction can be conducted at lower temperatures and at faster polymerization rates heretofore unattainable in lactone polymerization art.

Accordingly, one or more of the following objects will be achieved by the practice of this invention.

It is an object of this invention to provide a novel process for homopolymerizing monomeric cyclic esters to produce useful homopolymers. It is another object of this invention to provide anovel process for polymerizing an admixture containing at least two different monomeric cyclic esters to produce useful polymers. A further object of the invention is to prepare lactone polymers having a high degree of utility and application in 1 Collected Papers of Wallace H. Carothers, edited by H. Mark and G. S, 87)l1ltby, volume I, Interscrence Publishers,

I N w York 194 F. 5. van N-(itta. J. W. Hill, and W. H. Carothers, Jour.

Chem. Soc., 56, 455 (1934).

3,021,315 Patented Feb. 13, 1962 wherein each R, individually, can be hydrogen, alkyl, aryl, alkaryl, aralkyl, cycloalkyl, halo, haloalkyl, alkoxyalkyl, alkoxy, aryloxy, and the like; wherein A can be an oxy (O) group, a thio (-S) group, a divalent saturated aliphatic hydrocarbon group, and the like; wherein x is an integer from 1 to 15 inclusive; wherein y is an integer from 1 to 15 inclusive; wherein z is an integer having a value of zero or one; with the provisos that (a) the sum of x+y+z cannot equal 3, (b) the total number of atoms forming the cyclic ester ring does not exceed 18, preferably does not exceed 9, (c) the total number of organic substituents (such as those described for the R variables) attached to the carbon atoms contained in the cyclic ester ring does not exceed 4, preferably does not exceed 3, (d) from 2 to 4 continuously linked carbon atoms contained in the cyclic ester ring can represent a portion of a saturated cycloaliphatic hydrocarbon nucleus which contains from 4 to 10 ring carbon atoms, and (e) the four R variables attached to any two adjacent carbon atoms contained in the cyclic ester ring can represent a portion of a fused aromatic hydrocarbon nucleus.

With reference to Formula I supra, illustrative R radicals include, among others, methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, t-butyl, amyl, the hexyls, the heptyls, the octyls, dodecyl, octade cyl, phenyl, benzyl, tolyl, xylyl, ethylphenyl, butylphenyl, phenethyl, phenylpropyl, phenylbutyl, cyclopentyl, 2-propylcyclohexyl, cyclohexyl, Z-methylcyclohexyl, cycloheptyl, chloromethyl, chloroethyl, bromopropyl, bromobutyl, chloro, fluoro, bromo, iodo, methoxymethyl, ethoxyethyl, propoxymethyl, butoxypropyl, methoxy, ethoxy, n-propoxy, nbutoxy, isopentoxy, n-hexoxy, Z-ethylhexoxy, 3-methyloctoxy, decoxy, dodecoxy, octadecoxy, phenoxy, ethylphenoxy, propylphenoxy, dimethylphenoxy, phenylpropoxy, and the like. It is preferred that each R, individually, be hydrogen, alkyl, and/or alkoxy, and preferably still, that each R, individually, be hydrogen, lower alkyl, e.g., methyl, ethyl, n-propyl, isobutyl, and/or.lower alkoxy, e.g., methoxy, ethoxy, propoxy, n-butoxy, and the like. It is further preferred that the total number of carbon atoms in the substituents attached to the cyclic II C A gamma-butyrolactone Prior art attempts to polymerize gamma-butyrolactone and the substituted gamma-butyrolactones have been unsuccessful. Attempts to polymerize the cyclic esters, e.g., gamma butyrolactones, beta-oxa-gamma-butyrolactones, and the like, in the process of this invention likewise have failed. One would postulate that the thermodynamic stability of these monomeric cyclic esters which contain five atoms in the lactone ring is much greater than the corresponding polymers, and that the free energy of interconver'sion is exceedingly low. Proviso states that the total number of organic substituents attached to the carbon atoms contained in the cyclic ester ring should not exceed four, and preferably should not exceed three. It has been observed that when the total number of organic substituents on the cyclic ester ring approached four or 1 more, then the polymerizability of the cyclic ester monomer in the process of the invention diminished drastically. Proviso (d) states that from 2 to 4 continuously linked carbon atoms contained in the cyclic ester ring can represent a portion of 'a saturated cycloaliphatic hydrocarbon nucleus which contains from 4 to ring carbon atoms such as, for example, a saturated cycloaliphatic hydrocarbon nucleus derived from cycloalkane, alkyl-substituted 'cycloalkane, cyclobutane, cyclopentane, cyclohexane, cycloheptane, cyclooctane, methylcyclopentane, methylcyclohexane, and the like. Thus, for example, the following illustrative cyclic esters would be included in this proviso:

2-0xabicyclo [3.2.2]n'onau- 3 -one gProviso (e) states that the four R variables attached to any two adjacent carbon atoms contained in the cyclic ester ring can represent a portion of a fused aromatic hydrocarbon nucleus, that is, an aromatic nucleus derived from benzene, alkylbenzene, methylbenzene,- propylbenzene, naphthalene and the like. To illustrate thisproviso,

the following compound is depicted structurally.

2,3,4,5 tetral1ydro 2-ketobenzoxepi In the structurally depicted compound immediately above, the four R variables which were attached to the carbon atoms designated by numerals 6 and 11 now represent a portion of the fused benzene ring, namely the carbon W. H. Carothers. G. L. Borough. and F. J. van Natta, Jour. Amer. Chem. 800., 5'4, 761 '(1932').

4 atoms designated by the numerals 7, 8, 9 and 10. The following compound further illustrates proviso (e).

2-(2'-hydroxymethylpheny1)benzene carboxylic acid lactone Representative monomeric cyclic esters which can be employed as starting materials in the method of the invention include, for example, beta-propiolactone, delta-valerolactone, epsilon-caprolactone, 7-hydroxyheptanoic acid lactone, S-hydroxyoctanoic acid lactone, l2-hydroxydodecanoic acid lactone, 'l3-hydroxytridecanoic acid lactone, l4-hydroxytetradecanoic acid lactone, IS-hydroxypentadecanoic acid lactone, 16-hydroxyhexadecanoic acid lac tone, l7-hydroxyheptadecanoic acid lactone; the alpha, alpha-dialkyl-beta-propiolactones, e.g., alpha, alpha-dimethyl-beta-propiolactone, alpha, alpha-diethyl-beta-proa piolactone, alpha, alpha-dipropyl-beta-propiolactone, and the like; the monoalkyl-delta-valerolactones, e.g., the monomethylmonoethyl-, monoisopropyl-, monobutyi-, monohexyl-, monodecyl-, and Inonododecyl-delta-valero-- lactones, and the like; the dialkyl-delta-valerolactones in which the two alkyl groups are substituted on the same or difierent carbon atoms in the cyclic ester ring, e.g., the dimethyl-, diethyl-, diisopropyl-, dipentyl-, and di-n-octyldelta-valerola'ctones, and the like; the m0noa1kyl-, dialkyl-, or trialkyl-epsilon-caprolactones, e.g., the monomethyl-, monoethyl-, monoisopropyl-, monohexyl-, mono-n-octyl-, dime'thyl d'iethyl-, di-n-propyl-, diisobutyl-, di-n-hexyl-, trimethyl-, triethyl-, and tri-n-propyl-epsilon-caprolactones, and the like; the monoalkoxyand dialkoxy-deltavalerolactones and epsilon-caprolactones, e.g., monomethoxy-, monoethoxy-, monoisopropoxy-, dimethoxy diethoxy-, and dibutoxy-delta-valerolactones and epsilon-caprolactones, and the like. Further illustrative cyclic esters include 3-ethyl-2-keto-1,4 dioxane, gamma(l-isopropyl-4- methylcyclohexyl)-epsilon-caprolactone, 3-br0mo-2,3,4,5,'

. tetrahydrobenzoxepin-2-0ne, 2 (2' hydroxyphenyl)benzene carboxylic acid lactone, IO-hydroxyundeeanoic acid lactone, 2,5,6,7,-tetrahydrobenzoxepin-Z-one, 9-oxabicyclo[5.2.2]undecan-8-one, 4-oxa-14 hydroxytetradecanoic' acid lactone, alpha, alpha-bis(chloromethyl)-propiolactone, 1,4-dioxane-2-one, 3-n-propyl-2-keto-l,4 dioxane, 3- (Z-ethylhexyl)-2-keto-l,4-dioxane, and the like. Illustrative-subclasses of cyclic esters which are eminently suitable in the process of the instant invention include the unsubstituted lactones and the oxalactones which contain from 6 to 8 atoms in the lactone ring, preferably delta-valerolactone, *epsilon-caprolactone, the keto-dioxanes, and the like; the monoand polyalkyl-substituted lactones and oxalactones which contain from 6 to 8 atom-s in the lac tone ring, preferably the monoand poly-lower alkyl delta-valerolactones, epsilon-caprolactones, and their cor responding oxalactones wherein the alkyl substituent(s) contains from 1 to 4 carbon atoms, and the like; and the monoand polyalkoxy-substituted lactones and oxalactones which contain from 6 to 8 atoms in the lactone ring, preferably the monoand poly-lower alkoxy-delta-valero- "lactones, epsilon-caprolactones, and their corresponding oxalactones'wherein the alkoxy substituent(s) contains from 1 to 4 carbon atoms.

The unsubstituted and substituteddelta-valerolactones, epsilon-caprolactone's, 'zeta-enantholactones, and higher membered lactones, e.g.,monoand polyalkyl-substituted delta-valerolactones, monoand polyalkoxy-substituted delta-valerolactones, monoand polycycloalkyl-substituted delta-valerolactones, aryl-substituted delta-valerolactones, monoand polyhaloalkyl-substitute'd delta-Valeralactones, monoand polyalkyl-substituted 'epsi1q aprolactones, monoand polyalkoxy-epsilon-caprolactones, aryl-substituted epsilon-caprolactones, monoand polyhaloalkyl-substituted epsilon-caprolactones, monoand polyalkyl-substituted zeta-enantholactones, and various other lactones described previously can be prepared by reacting the corresponding cyclic ketone with an anhydrous solution comprising peracetic acid and acetone. It is desirable to add the peracetic acid solution to an excess of ketone, e.g., to 1 molar ratio of ketone to peracetic acid, in a still kettle maintained under reflux. The pressure can be adjusted so as to provide a kettle temperature of, for example, about 70 C. Acetone, acetic acid by-product, and minor amounts of ketone can be continuously removed throughout the addition period. Subsequently, the lactone product can be recovered from the still kettle by conventional techniques such as by distillation.

Stoll and Rouv report the preparation of lactones which contain up to 22 carbon atoms in the lactone nucleus by a process which comprises contacting the corresponding terminal hydroxy saturated aliphatic monocarboxylic acid with benzene-sulfonic acid catalyst in boiling benzene. These authors also report the preparation of other lactones such as 14-alkyl-14-hydroxytetradecanoic acid lactone, e.g., 14-hydroxypentadecanoic acid lactone, and oxa-15-hydroxypentadecanoic acid lactone, e.g., 12-oxa-IS-hydroxypentadecanoic acid lactone. Palornaa and Tonkola teach the preparation of 3-oxa-6- hydroxyhexanoic acid lactone by heating the corresponding terminal hydroxy saturated aliphatic monocarboxylic acid. The preparation of 2-keto-l,4-dioxane, 3-alkyl-2 keto-1,4-dioxane, polyalkoxy-substituted delta-valerolactone, alkoxyalkyl-substituted delta-valerolactone, etc., is recorded by Carothers et all The preparation of dialkyl-substituted, dihalo-substituted lactone, e.g., gamma, delta-dibromo-gamma, delta-dimethyl-delta-valerolactone is reported in the literature by Levina et al. German Pat. No. 562,827 discloses the preparation of 2,3,4,5- tetrahydrobenzoxepin-Z-one whereas the literature reports the position isomer, namely 2,5,6,7-tetrahydrobenzoxepin-Z-one. Cycloalkyl-substituted epsilon-caprolactone, e.g., gamma(1-isopropyl-4-methylcyclohexyl)-epsilon-caprolactone is disclosed by Belov and Kheifits McKay et al. have recorded the preparation of halosubstituted, haloalkyl-substituted delta-valerolactone. The literature also reports the preparation of various other cyclic esters.

The metal hydrides contemplated as catalysts in the process of the invention include the hydrides of Group IA metals of the periodic table, i.e., lithium hydride, potassium hydride, sodium hydride, rubidium hydride, and cesium hydride; and the alkaline earth metal hydrides, i.e., calcium hydride, strontium hydride, and barium hydride.

The catalysts are employed in catalytically significant quantities. In general, a catalyst concentration in the range of from about 0.001, and lower, to about 10, and higher, weight percent, based on the weight of total monomeric feed, is suitable. A catalyst concentration in the range of from about 0.01 to about 3.0 weight percent is preferred. A catalyst concentration in the range of from about 0.05 to about 1.0 weight percent is highly preferred. For optimum results, the particular catalyst employed, the nature of the monomeric reagent(s), the operative conditions under which the polymerization reaction is conducted, and other factors will largely determine the desired catalyst concentration.

The polymerization reaction can be conducted over a wide temperature range. Depending upon various factors such as the nature of the monomeric reagent(s) em- 5 Helv. Chim. Acta. 18, 1087 (1935).

6 Ben, 66, 1629 (1933).

7 See footnote 1.

5 Zhur, Obshchei Khim, 24, 1439 (1934). Ben, 68B. 1170 (1935). J. Gen. Chem. USSR, 27, 1459 (1957). J. Amer. Chem. Soc. 77, 5601-6 (1955).

ployed, the particular catalyst employed, the concentration of the catalyst, and the like, the reaction temperature can be as low as 40 C., and lower, and as high as 250 C., and higher. A suitable temperature range is from about 20 to about 225 C. A reaction temperature in the range of from about 0 to about 200 C. is preferred.

The polymerization reaction preferably occurs in the liquid phase, and to this extent sufficient pressure is employed to maintain an essentially liquid reaction mixture regardless whether or not an inert normally-liquid organic vehicle is employed. Preferably, the polymerization reaction is conducted under an inert atmosphere, e.g., nitrogen, butane, helium, etc. The ultimate molecular Weight of the resulting polymer will depend, to an extent, upon various factors such as the temperature, the choice and concentration of the catalyst, the use and amount of an inert normally-liquid organic vehicle(s), and the like.

In general, the reaction time will vary depending on the operative temperature, the nature of the monomeric cyclic esters employed, the particular catalyst and the concentration employed, the use of an inert normallyliquid organic vehicle, and other factors. The reaction time can vary from several seconds to several hours, or more, depending on the variables illustrated above.

It is preferred to conduct the polymerization reaction in the essential absence of impurities which contain active hydrogen since the presence of such impurities tends to deactivate the catalyst and/ or increase the induction period. The minimization or essential avoidance of impurities such as water, carbon dioxide, aldehydes, ketones, etc., is highly desirable. It is also preferred that the polymerization reaction be conducted under substantially anhydrous conditions.

When polymerizing an admixture containing at least two difierent cyclic esters, the proportions of said cyclic esters can vary over the entire range. Broadly the concentration of each monomeric cyclic ester is in the range of from about 3 to about 97 weight percent, based on the total weight of said cyclic esters. The preferred range is from about 15 to about weight percent. Admixtures containing epsilon-caprolactone and monoand/ or polyalkyl-substituted epsilon-caprolactone (including isomeric mixtures thereof) are highly preferred as starting mate rials in the process of the invention. Admixtures containing difierent monoand/ or polyalkyl-substituted epsiloncaprolactones (including isomeric mixtures of the same and/or difierent monoand/or polyalkyl-substituted epsilon-caprolactones) also are highly preferred.

The polymersof this invention can be prepared via the bulk polymerization, suspension polymerization, or the solution polymerization routes. The polymerization reaction can be carried out in the presence of an inert normally-liquid organic vehicle such as, for example, aromatic hydrocarbons, e.g., benzene, toluene, xylene, ethylbenzene, and the like; various oxygenated organic compounds such as anisole, the dimethyl and diethyl ethers of ethylene glycol, of propylene glycol, of diethylene glycol and the like; normally-liquid saturated hydrocarbons including the open chain, cyclic, and alkyl-substituted cyclic saturated hydrocarbons such as hexane, heptane, various normally-liquid petroleum hydrocarbon fractions, cyclohexane, the alkylcyclohexanes, decahydronaphthalene, and the like. If desired, a mixture of mutually miscible inert normally-liquid organic vehicles can be employed.

The process of the invention can be executed in a batch, semi-continuous, or continuous fashion. The reaction vessel can be a glass vessel, steel autoclave, elongated metallic tube, or other equipment and material employed in the polymer art. The order of addition of catalyst and monomeric reagent(s) does not appear to be critical. A suitable procedure is to add the catalyst to the reaction zone containing the monomeric reagent(s) and inert organic vehicle, if any. It is highly preferred that the catalyst be added as a suspension or dispersion in an inert normally-liquid organic vehicle such as, for instance, the inert normally-liquid saturated aliphatic and cycloali! phatic hydrocarbons, e.g., hexane, heptane, octane, cyclohexane, alkylcyclohexane, decahydronaphthalene, and the like. Incremental addition of catalyst to the reaction zone can be employed. If desired, the above procedure can be reversed, that is, themonomeric reagent(s) perse oras a solution or suspension in an inert organic vehicle can be added to the reactionzone which preferably contains the catalyst as a suspension or dispersion in aninert normallyliquid organic vehicle. Also, the catalyst, reagent(s), and inert organic vehicle, if any, can be added to the reaction zone simultaneously. The reaction zone (be it a closed vessel or an elongated tube) can be fitted with an external heat exchanger to thus control undue temperature fluctuations, or to prevent any possible run-away reaction temperatures due to the exothermic nature of the reaction. In a continuous operation employing as the reaction zone an elongated tube or conduit, the use of one or a plurality of separate heat exchangers can be conveniently used. In a batch operation, stirring means can be provided for agitating the reaction mixture, as desired.

Unreacted monomeric reagent oftentimes can be recovered from the reaction product by conventional techniques such as by heating said reaction product under reduced pressure. Removal of unreacted monomeric reagent(s) and/or inert organic vehicle can be accomplished by mechanical means such as treatment of the reaction product in .a Marshall Mill and the like. The polymer product also can be recovered from the reaction product by washing said reaction product with an inert normallyliquid organic vehicle, e.g., heptane, and subsequently drying same under reduced pressure at slightly'elevated temperatures. Another route involves dissolution in a first inert organic vehicle, followed by the additionof a second inert organic vehicle which is miscible with the first vehicle but which is a non-solvent for the polymer product, thus precipitating the polymer product. If desired, the reaction product can be dissolved in an inert organic vehicle such as acetone, and the like, followed by theaddit-ion of suificient waterto the resulting solution, said water being miscible with said inert organic vehicle but being a non-solvent for the water-insoluble polymer thereby precipitating the polymer product. Recovery of the precipitated polymer can be effected by filtration, decantation, etc., followed by dryingsame as indicated pre- Yiously.

The linear polyester products resulting from the P jocess of the invention can be characterized by the following recurring structural unit:

wherein the variables R, A, x, y, and 2, have the same values as shown in Formula I supra. ,Of course, the five provisos enumerated as (a) through (e) set forth in the discussion of Formula I supra likewise apply to the structural unit designated as Formula II above. In addition, as indicated previously, the molecular weights of the polyester products can range from about several hundred to about several thousand. The ultimate molecular weight and properties of the polyester products will depend, in the main, upon the choice of the cyclic ester(s) and catalyst, the concentration of the catalyst, the operative conditions employed, e.g., temperature, etc., the purity of the monomeric reagent(s) and catalyst, the use and amount of an inert normally-liquid organic vehicle,

and the .like.

It is readily apparent that the linearhomopolymers are essentially characterized by the same recurring unit which falls within the scope of Formula II supra. The copolymers, terpolymers, etc., on the other hand, can contain as little as 1.0 weight percent, and lower, and upwards to 99 weight percent, and higher, of the same recurring unit. Desirable polymers are those in which the weight percent of the different recurring units is in the range of from about 3 to about 97. In the highly preferred copolyrners the weight percent of the two difierent recurring units isin the range of from about 15 to about 85.

The polymers obtained by the process of the invention are a useful class of polyester compounds. These polymers can range from viscous liquids to tough solids. The polymers in the range of from very viscous liquids to relatively low molecular weight, wax-like solids are useful in the preparation of cosmetics, polishes, and waxes, and as thickening agents for various lubricants. The polymers can be employed to size cellulosic material or they can be used as anti-static agents in the treatment of fibrous materials. They can also be employed as protective coatings, and/or impregnants. The solid polymers are useful for the production of various shaped articles such as brush handles, buttons, lamp bases, toys, and the like. The solid polymers are useful in the preparation of films by such techniques as milling on a two-roll mill, calendering, solvent casting, and the like.

In passing, it should be notedthat one apparent advantage aflorded by the practice of the invention is the preparation of copolymers, terpolymers, etc., whose physical characteristics can be tailor-made to fit desired fields of applications and uses. In other words, by adjusting the concentration of themonomeric charge to a particular polymerization system, copolymers, terpolymers, etc., which cover a wide spectrum of properties and characteristics can be prepared, e.g., soft, rubbery polymers to tough, solid polymers.

In the illustrative operative examples to follow, the polymeric product oftentimes is described as possessing a certain reduced viscosity value. By this term, i .e., reduced viscosity, is meant a value obtained by dividing the specific viscosity by the concentration of the polymer in the solution, the concentration being measured in grams of polymer per 100 milliliters of solvent at a given temperature. The specific viscosity is obtained by dividing the difference betweenthe viscosity of the solution and the viscosity of the solvent by the viscosity of the solvent. The reduced viscosity value is an indication of the molecular weight of the polymer. Unless otherwise indicated, the reduced viscosity value was determined at 30 C.

Also, in the illustrative operativeexample below, the polymerization reaction was generally conducted under an inert atmosphere, e.g., nitrogen. The reaction vessel and contents, i.e., cyclic ester(s'), catalyst, and inert organic vehicle, if any, were maintained, usually under agitation, in a constant temperature, e.g., 90 C., or the reaction vessel containing the cyclic ester(s) was maintained, usually under agitation, in a constant temperature and subsequently the catalyst vwas added thereto. Since the polymerization reaction, in general, was exothermic a rise in temperature was observed, e.g., to C. In several instances the period recorded was the time observed in which the rotation of the mechanical stirrer ceased due to the high viscosity of the contents in the reaction vessel. In'most cases the reaction vessel was left in the constant temperature bath for an additional period of time, e.g., about 20 minutes, or longer. Unless otherwise indicated, the examination ordescription of the polymeric product was conducted at room temperature, i.e., about 23 C. In general, the conversion of monomer to polymer was substantially quantitative.

EXAMPLE 1 (A) To a reaction vessel maintained under a nitrogen atmosphere and which contained epsilon-caprolactone,

there was charged sodium hydride in an amount so as to give an admixture containing 0.33 weight percent sodium hydride, based on the weight of said epsilon-caprolactone. The reaction vessel then was placed in a constant temperature bath maintained at 90 C. Within 77 minutes the mechanical stirrer ceased due to the high viscosity of the contents in the reaction vessel. Thereafter, the polymeric product was recovered. There was obtained a white, soft, rubbery solid homopolymer which possessed a reduced viscosity value of 0.46 (measured at 0.4 gram of polymer in 100 ml. of chloroform).

(B) In an analogous manner as above, when beta, gamma-dimethoxy-delta-valerolactone is substituted for epsilon-caprolactone and contacted with 1.0 weight percent calcium hydride, there is obtained a solid polymer.

EXAMPLE 2 (A) To a reaction vessel maintained under a nitrogen atmosphere and which contains epsilon-caprolactone, there is charged sodium hydride in an amount so as to give an admixture containing 0.5 weight percent sodium hydride, based on the weight of said epsilon-caprolactone. The reaction vessel then is placed in a constant temperature bath maintained at 90 C. for a period of 45 minutes. Thereafter, the reaction product is dissolved in chloroform and reprecipitated in petroleum ether. There is obtained a solid homopolymer. a

(B) In an analogous manner as above, when lithium hydride is substituted for sodium hydride in an amount so as to give an admixture which contains 1.0 weight percent of lithium hydride, based on the weight of epsiloncaprolactone, essentially the same results are obtained.

EXAMPLE 3 (A) To a reaction vessel maintained under a nitrogen atmosphere and which contains epsilon-caprolactone, there is charged sodium hydride dispersed in cyclohexane in an amount so as to give an admixture containing 0.7 weight percent sodium hydride, based on the weight of said epsilon-caprolactone. The reaction vessel then is placed in a constant temperature bath maintained at 90 C. Within 5 minutes the mechanical stirrer ceased due 10 rubidium hydride, based on the total weight of methylepsilon-caprolactone. The isomeric mixture contains by weight, approximately 30 percent gamma-methyl-epsiloncaprolactone, about 30 percent epsilon-methyl-epsiloncaprolactone, and about 40 percent beta-methyland deltamethyl-epsilon-caprolactone. This isomeric lactone mixture is prepared by reacting a mixture of 2-methyl-, 3- methyl-, and 4-methylcyclohexanone with peracetic acid. The reaction vessel then is placed in a constant temperature bath maintained at 90 C. for a period of 30 minutes.

' Thereafter, the polymeric product is recovered. There is to the high viscosity of the contents in the reaction vessel;

Thereafter, the polymeric product is recovered. There is obtained a tough, solid product.

(B) In an analogous manner as above, when gamma( l-isopropyl 4-methylcyclohexyl)-epsilon-caprolactone is substituted for epsilon-caprolactone and contacted with 0.7 weight percent potassium hydride (dispersed in heptane), a viscous liquid product is obtained.

EXAMPLE 4 (A) To a reaction vessel maintained under a nitrogen atmosphere and which contains epsilon-caprolactone,

there is charged sodium hydride dispersed in hexane in an amount so as to give an admixture containing 0.6 weight percent sodium hydride, based on the weight of said epsilon-caprolactone. The reaction vessel then is placed in a constant temperature bath maintained at 90 C. Within 4 minutes the mechanical stirrer ceased due to the high viscosity of the contents in the reaction vessel. Thereafter, the polymeric product is recovered from the reaction vessel. There is obtained a white, tough, solid homopolymer.

(B) In an analogous manner as above, when gammamethyl-delta-isopropyl-epsilon-caprolactone is substituted for epsilon-caprolactone and contacted with 1.0 weight percent lithium hydride, there is obtained a viscous liquid product.

EXAMPLE 5 (A) To a reaction vessel maintained under a nitrogen atmosphere and which contains an isomeric mixture of methyl-epsilon-caprolactone, there is charged rubidium hydride dispersed in petroleum ether in an amount so as to give an admixture containing 0.5 weight percent obtained a viscous liquid product.

(B) In an analogous manner as above, when 2-bromo- 2-(3'-bromopropyl)-5-hydroxypentanoic acid lactone is substituted for the isomeric mixture of methyl-epsilonc-aprolactones and contacted with 1.0 weight percent barium hydride, substantially similar results are obtained.

EXAMPLE 6 (A) To a reaction vessel maintained under a nitrogen atmosphere an which contains an isomeric mixture composed of a major proportion by weight of gamma-octylepsilon-caprolactone and a minor proportion by weight of epsilon-octyl-epsilon-caprolactone, there is charged sodium hydride dispersed in hexane in an amount so aS to give an admixture containing 0.8 weight percent sodium hydride, based on the total weight of octyi-epsiloncaprolactone. The reaction vessel then is placed in a constant temperature bath maintainedat C. for a period of 15 minutes. There is obtained a solid product.

(B) In an analogous manner as above, when 2,3, 1,5- tetrahydrobenZoXepin-2 one is substituted for the isomeric mixture of octyl-epsilon-caprolactones and contacted with 1.0 weight percent potassium hydride, there is obtained a solid polymer.

EXAMPLE 7 (A) To a reaction vessel maintained under a nitrogen atmosphere and which contains delta-vaierolactone, there is charged lithium hydride dispersed inpetroleum ether in an amount so as to give an admixture containing 0.5 weight percent lithium hydride, based on the weight of said delta valerolactone. The reaction vessel thenis placed in a constant temperature bath maintained at 90 for a period of 30 minutes. Thereafter, the polymeric product is recovered. There is, obtained a hard, solid homopolymer.

(B) In an analogous manner as above, when 3-ethyl-2- keto-I,4-dioxane is substituted for delta-valerolactone and contacted with 1.0 weight percent calcium hydride, a viscous liquid is obtained.

EXAMPLE 8 (A) To a reaction vessel maintained under a nitrogen atmosphere and which contains beta-methyl-delta-valerolactone (redistilled, boiling point 137 C. at 1.5 mm. of Hg; :1 of 1.4480) there is charged sodium hydride dispersed in cyclohexane in an amount so as to give an admixture containing l.0 weight percent sodium hydride, based on the weight of said beta-methyl-delta-valerolactone. The reaction vessel then is placed in a constant temperature bath which is maintained at 90 C. for a period of about 30 minutes. Thereafter, the polymeric product is recovered. There is obtained a very viscous liquid product.

(B) In an analogous manner as above, when 3-oxa-6- hydroxy-hexanoic acid lactone is substituted for betamethyl-delta-valerolactone and contacted with 0.6 weight percent strontium hydride, essentially similar results are obtained.

EXAMPLES 9-11 the presence of sodium hydride dispersed in petroleum ether. The procedure employed is similarto thatset forth immediately preceding the operative examples. The

pertinent ,data and results are recorded in Table I below.

tal weight of the lactone feed. The procedure employed is similar to that set forth immediately preceding the op.

1 Weight percent catalyst, based on total weight of lactone charge.

N'rE.-Beta-methyl'delta-valerolactone redistilled; B.P. 137 0. at 1.5 mm. of Hg; 12

EXAMPLE 12 (A) To a reaction vessel maintained under a nitrogen atmosphere and which contains zeta-enantholactone, there is charged sodium hydride dispersed in heptane in an amount so as to give an admixture containing 0.5 weight percent sodium hydride, based on the weight of said zetaenantholactone. The reaction vessel then is placed in a -constant temperature bath maintained at 90 C. for a period of minutes. Thereafter, the polymeric product is recovered. There is'obtained a white, solid homopolymer.

(B) In an analogous manner as above, when -hydroxyundecanoic acid lactone is substituted for zetaenantholactone and contacted with 0.7 weight percent calcium hydride, essentially similarresults are obtained.

EXAMPLES 13-14 In Examples 13 and 14, the procedure employed is similar to that set forth immediately preceding the operative examples. The pertinent .data and results are re- Ratio is inparts by weight.

EXAMPLE 18 (A) To a reaction vessel maintained under a nitrogen atmosphere and which contains a mixture of 80 parts by weight of epsilon-.caprolactone and 20 parts by Weight of mixed dimethyl-epsilon-caprolactone, there is charged sodium hydride dispersed in hexane in .an amount so as to give an admixture containing 0.5 weight percent sodium corded in Table II.below. hydride, based on the total weight of the lactone feed.

T able ll Catalyst v Descrip- Example Lactone Charge 1 Catalyst 1 Concen- Temp., Tim tion of Number tration 3 0. Min. Polyester 13 30 zeta-enantholactoneflt] epsilon- NaH 0.50 90 10, Tough, caprolactone. wll ite I s01 "14; 20 zeta-enantholactone/80 epsilon- Cali, 0. 190 10 Do.

caprolactone.

Admixture of two lactones is expressed as parts by weight.

3 Catalystdispersed in petroleum ether.

3 Weight percent catalyst, based on total weight of lactone charge.

No'rE.Zeta-enantholactone redistilled; B.P. 72

EXAMPLE 15 (A) To a reaction vessel maintained under a nitrogen atmosphere and which contains 2-keto-1,4-dioxane, there is charged sodium hydride dispersed in petroleum ether in an amount so as to give an admixture containing 0.5 weight percent sodium hydride, based on the weight of said 2-ketc-l,4-dioxane. The reaction vessel then is placed in a constant temperature bath maintained at 90 C. for a period of about one hour. Thereafter, the polymeric product is recovered. There is obtained a solid polymer.

(B) In an analogous manner as above, when gamma- (1-isopropyl-4-methylcyclohexyl)-epsilon-caprolactone is substitued for 2-keto-1,4-dioxane and contacted with 1.0 weight percent lithium hydride, essentially similar results are obtained.

EXAMPLES 16-17 In Examples 16 and 17, various copolymers are prepared by contacting, at 90 C., a mixture of epsilon-capro lactone and delta-valerolact'one with 0.5 weight percent sodium hydride (dispersed in heptane), based on the to- C. at 4 mm. of Hg nnmof 1.4689.

The mixed dimethyl-epsilon-caprolactones is an isomeric mixture of beta,gamma-dimethyland gamma,delta-dimethyl-epsilon-caprolactones. The reaction vessel then is placed in a constant temperature bath maintained at C. fora period of 3 hours. Thereafter, the polymeric product is recovered. There is obtained a soft, solid product.

(B) In an analogous manner as above, when equal parts by weight of l2-oxa-l5-hydroxypentadecanoic acid lactone and 7-hydroxyheptanoic acid lactone are employed as the monomeric feed and contacted with 1.0 weight percent barium'hydride (dispersed in heptane), a viscous liquid is obtained.

7 EXAMPLE I9 (A) To a reaction vessel maintained under anitrogen atmosphere and which contains a mixture of 50 parts by weight of epsilon-caprolactone and 50 parts by weight of mixed octyl-epsilon-caprolactones, there is charged sodium hydride dispersed in cyclohexane in an amount so as to give an admixture containing 0.5 weight percent sodium hydride, based on the total weight of thelactone feed.

- epsilon-caprolactone The mixed octyl-caprolactones comprises a major proportion by weight of gamma-octyland a minor proportion by weight of epsilon-octyl-epsilon-caprolactones. The reaction vessel then is placed in a constant temperature bath maintained at 90 C. for a period of 1.5 hours. Thereafter, the reaction product is dissolved in acetone and reprecipitated in water. There is obtained a waxy EXAMPLE 20 To a reaction vessel maintained under a nitrogen atmosphere and which contains equal parts, by weight, of 2,4-dimethyl 4 methoxymethyl-S-hydroxypentanoic acid lactone and epsilon-caprolactone, there is charged sodium hydride (dispersed in decahydronaphthalene) in an amount so as to give an admixture containing 0.5 weight percent sodium hydride, based on .the total weight of the monomeric charge. The reaction vessel then is placed ,in a constant temperature bath maintained at 90 C. for .a period of 1 hour. Thereafter, the reaction product is dissolved in acetone and reprecipitated in water. There :is obtained a very viscous liquid copolymer.

EXAMPLE 21 (A) To a reaction vessel maintained under a nitrogen atmosphere and which contains ortho-(2-hydroxyethyl)- phenylacetic acid lactone, there is charged sodium hydride dispersed in heptane in an amount so as to give an admixture containing 0.50 weight percent sodium hydride, based on the weight of said ortho-(Z-hydroxyethyl)-phenylacetic acid lactone. The reaction vessel then is placed in a constant temperature bath maintained at 90 C. for a period of 30 minutes. There is obtained a soft, solid polymer.

(B) In an analogous manner as above, when cis-3-oxabicyclo[5.4.0]undecan-4-one is substituted for ortho(2-hydroxyethyl)phenylacetic acid lactone and contacted with 1.0 weight percent calcium hydride, essentially similar results are obtained.

EXAMPLE 22 To a reaction vessel maintained under a nitrogen atmosphere and which contained epsilon-caprolactone, there was charged sodium hydride (dispersed in benzene) in an amount so as to give an admixture containing 0.2 weight percent sodium hydride, based on the weight of said epsilon-caprolactone. The reaction vessel then was placed in a constant temperature bath maintained at 90 C. Within 3 minutes the mechanical stirrer ceased due to the high viscosity of the contents in the reaction vessel. Thereafter, the polymer was recovered. There was obtained a tough, solid homopolymer which possessed a reduced viscosity value of 0.78 (measured at 0.2 gram of polymer in 100 ml. of chloroform).

EXAMPLE 23 To a reaction vessel maintained under a nitrogen atmosphere and which contained 50 parts by weight of and 60' parts by weight of gamma-octyl-epsilon-caprolactone, there was charged sodium hydride (dispersed in benzene) in an amount so as to give an admixture containing 0.2 weight percent sodium hydride, based on the weight of the total lactone feed. The reaction vessel then was placed in a constant temperature bath maintained at 90 C. Within 3 minutes the mechanical stirrer ceased due to the high viscosity of the contents in the reaction vessel. Thereafter, the polymer was recovered. There was obtained a soft, semicrystalline solid which possessed a reduced viscosity value of 0.81 (measured at 0.2 gram of polymer in -100 ml. of

chloroform). t

' 14 EXAMPLE 24 To a reaction vessel maintained under a nitrogen atmosphere and which contained epsilon-caprolactone, there was charged calcium hydride (dispersed in benzene) in an amount so as to give an admixture containing 0.2 weight percent calcium hydride, based on the weight of said epsilon-caprolactone. The reaction vessel then was placed in a constant temperature bath maintained at C. for a period of 3 hours. Thereafter, the polymer was recovered. There was obtained a soft, waxy, solid homopolymer which possessed a reduced viscosity value of 0.36 (measured at 0.2 gram of polymer in m1. of chloroform).

Although the invention has been illustrated by the preceding examples, the invention is not to be construed as limited to the materials employed in the above exemplary examples, but rather, the invention encompasses the generic area as hereinbefore disclosed. Various modifications and embodiments of this invention can be made without departing from the spirit and scope thereof.

What is claimed is:

1. A process which comprises polymerizing a cyclic ester characterized by the following formula:

wherein each R, individually, is selected from the group consisting of hydrogen, alkyl, aryl, alkaryl, aralkyl, cycloalkyl, halo, haloalkyl, alkoxyalkyl, alkoxy, and aryloxy; wherein A is-selected from the group consisting of an oxy group, a thio group, and a divalent saturated aliphatic hydrocarbon group; wherein x is an integer in the range of from 1 to 15 inclusive; wherein y is an integer in the range of from 1 to 15 inclusive; and wherein z is an integer selected from the group consisting of zero and one; with the provisos that (a) the sum of x+y+z cannot equal three, (1)) the total number'of atoms forming the cyclic ester ring does not exceed 18, (c) the total number of organic substituents attached to the carbon atoms contained in the cyclic ester ring does not exceed four, (d) from 2 to 4 continuously linked carbon atoms contained in the cyclic ester ring can represent a portion of a saturated cycloaliphatic hydrocarbon nucleus which nucleus contains from 4 to 10 carbon atoms, and (e) the four R variables attached to any two adjacent carbon atoms contained in the cyclic ester ring can represent a portion of a fused aromatic hydrocarbon nucleus; with from about 0.001 to about 10 weight percent, based on the total weight of cyclic ester, of a metal hydride selected from the group consisting of lithium hydride, potassium hydride, sodium hydride, rubidium hydride, cesium hydride, calcium hydride, strontium hydride, and barium hydride; under substantially anhydrous conditions; for a period of time sufii- -cient to produce a polymer.

2. A process which comprises polymerizing an admix- .ture comprising at least two difierent cyclic esters which are characterized by the following formula:

wherein each R, individually, is selected from the group ing of an oxy group, a thio group, and a divalent saturated aliphatic hydrocarbon group; wherein x is an 'integer in the range of from 1 to 15 inclusive; wherein y is an integer in the range of from 1 to 15 inclusive;

and wherein z is an integer selected from the group consisting of zero and one; with the provisos that (a) the sum of x+y+z cannot equal three, (b) the total number of atoms forming the cyclic ester ring does not exceed '18, (c) the total number of organic substituents attached to the carbon atoms contained in the cyclic ester ring does not exceed four, (d) from 2 to 4 continuously linked carbon atoms contained in the cyclic ester ring can represent a portion of a saturated cycloaliphatic hydrocarbon nucleus which nucleus contains from 4 to 10 carbon atoms, and (e) the four R variables attached to any two adjacent carbon atoms contained in hte cyclic ester ring can represent a portion of a fused aromatic hydrocarbon nucleus; with from about 0.001 to about 10 weight percent, based on the total weight of cyclic ester, of a metal hydride selected from the group consisting of lithium hydride, potassium hydride, sodium hydride, rubidium hydride, cesium hydride, calcium hydride, strontium hydride, and barium hydride; under substantially anhydrous conditions; for a period of time suflicient to produce a polymer.

3. A process which comprises polymerizing deltavalerolactone with from about 0.01 to about 3.0 weight percent, based on the weight of said delta-valerolactone, of a metal hydride selected from the group consisting of lithium hydride, potassium hydride, sodium hydride, rubidium hydride, cesium hydride, calcium hydride, strontium hydride, and barium hydride; at a temperature in the range of from about C. to about 225 C.; under substantially anhydrous conditions; for a period of time suflicient to produce a polymer.

4. The process of claim 3 wherein said metal hydride is a group IA metal hydride.

5. The process of claim 3 wherein said metal hydride is an alkaline earth metal hydride.

6. A process which comprises polymerizing an alkylsubstituted delta-valerolactone with from about 0.0l to about 3.0 weight percent, based on the weight of said alkyl-substituted delta-valerolactone, of a metal hydride selected from the group consisting of lithium hydride, potassium hydride, sodium hydride, rubidiumrhydride, cesium hydride, calcium hydride, strontium hydride, and barium hydride; at a temperature in the range of from about 20 C. to about 225 C.; under substantially anhydrous conditions; .for a period of time sufiicient to produce a polymer.

7. A process which comprises polymerizing epsiloncaprolactone with from about 0.01 to about 3.0 weight percent, based on the Weight of said epsilon-caprolactone, of a metal hydride selected from'the groupconsisting of lithium hydride, potassium hydride, sodium hydride, rubidium hydride, cesium hydride, calcium hydride, strontium hydride, and barium hydride; ata temperature in the range of from about -20 C..to about 225 C.; under substantially anhydrous conditions; and for a period of time sufficient to produce a. polymer.

. 8. The process of claim 7 wherein said metal hydride is a group IA metal hydride.

9. The process of claim 7 wherein. said metal hydride .is an 'alkalineearth metal hydride.

10. A process which comprises polymerizing an alkylsubstituted epsilon-caprolactone with from about 0.01 to about 3.0 weight percent, based on the weight of said alkyl-substituted epsilon-caprolactone, of a metal hydride selected from the group consisting of lithium hydride, potassium hydride, sodium hydride, rubidium hydride, cesium hydride, calcium hydride, strontium hydride, and bariumhydride; at a temperature in the range of from about -20" C. to about 225 C.; under substantially anhydrous conditions; and for a to produce a polymer.

11. The process of claim' 10 wherein said metal hydride is a group IA metal hydride.

12. The process of claim 10 wherein said metal hydride is :an alkaline earth metal hydride.

period of time sutficient 13. A process which comprises polymerizing a monoand an alkyl-substituted delta-valerolactone with from about 0.01 to, about 3.0 weight percent, based on the total weight of the monomeric lactone feed, of a metal hydride selected from the group consisting of lithium hydride, potassium hydride, sodium hydride, rubidium hydride, cesium hydride, calcium hydride, strontium hydride, and barium hydride; at a temperature in the range of from about 20 C. to about 225 C.; under substantially anhydrous conditions; and for a period of time sufficient to produce a polymer.

14. The process of claim 13 wherein said metal hydride is a group IA metal hydride.

15. The process of claim 13 wherein said metal hydride is an alkaline earth metal hydride.

16. A process which comprises polymerizing a monomeric lactone admixture comprising delta-valerolactone and epsilon-caprolactone with from about 0.1 to about 3.0 weight percent, based on the total weight of the monomeric lactone feed, of a metal hydride selected from the group consisting of lithium hydride, potassium hydride, sodium hydride, rubidium hydride, cesium hydride, calcium hydride, strontium hydride, and barium hydride; at a temperature in the range of from about -20 C. to about 225 C.; under substantially anhydrous conditions; and for a period of time suflicient to produce a polymer.

17. The process of claim 16 wherein said metal hydride is a group IA metal hydride.

18. The process of claim .16 wherein said metal hydride is an alkaline earth metal hydride.

19. A process which comprises polymerizing a monomeric lactone admixture comprising delta-valerolactone and an alkyl-substituted epsilon-caprolactone with from about 0.01 to about "3.0 weight percent, based on the total weight of the monomeric lactone feed, of a metal hydride selected from the group consisting of lithium hydride, potassium hydride, sodium hydride, rubidium hydride, cesium hydride, calcium hydride, strontium hydride, and barium hydride; at a temperature in the range of from about 20 C. to about 225 C.; under substantially anhydrous conditions; and for a period of time sufiicient to produce a polymer.

20. The process of claim 19 wherein said metal hydride is a group IA metal hydride.

21. The process of claim 19 wherein said metal hydride is an alkaline earth metal hydride.

22. A process which comprises polymerizing a monomeric lactone admixture comprising epsilon-caprolactone and an alkyl-substituted 'delta-valerolactone with from about 0.01 to about 3.0 weight percent, based on the total weight of the monomeric lactone feed, of a metal hydride selected from the group consisting of lithium hydride, potassium hydride, sodium hydride, rubidium hydride, cesium hydride, calcium hydride, strontium hydride, and barium hydride; at a temperature in the range of from about 20 C. to about 225 C.; under substantially anhydrous conditions; and for a period of time sufiicient to produce a polymer.

23. The process of claim 22 wherein said metal hydride is a group IA metal hydride.

24. The process of claim 22 wherein said metal hydride is an alkaline earth metal hydride.

25. A process which comprises polymerizing a monomeric lactone admixture comprising epsilon-caprolactone and an alkyl-substituted epsilon-caprolactone with from about 0.01 to about 30 weight percent, based on the total weight of the monomeric lactone feed, of a metal hydride selected from the group consisting of lithium hydride, potassium hydride, sodium hydride, rubidium hydride, cesium hydride, calcium hydride, strontium hydride, and barium hydride; at a temperature in the range 26. A process which comprises polymerizing a monomeric laetone admixture comprising an alkyl-substituted epsilon-caprolactone and an alkyl-substituted delta-valerolactone with from about 0.01 to about 3.0 weight percent, based on the total weight of the monomeric lactone feed, of a metal hydride selected from the group consisting of lithium hydride, potassium hydride, sodium hydride, rubidium hydride, cesium hydride, calcium hydride, strontium hydride, and barium hydride; at a temperature in the range of from about 20 C. to about 225 C., under substantially anhydrous conditions; and for a period of time sufficient to produce a polymer.

27. The process of claim 26 wherein said metal hydride is a group 1A metal hydride.

28. The process of claim 26 wherein said metal hydride is an alkaline earth metal hydride.

29. A process which comprises polymerizing a monomeric lactone admixture comprising two different alkylsubstituted delta-valerolactones with from about 0.1 to about 3.0 weight percent, based on the total weight of the monomeric lactone feed, of a metal hydride selected from the group consisting of lithium hydride, potassium hydride, sodium hydride, rubidium hydride, cesium hydride, calcium hydride, strontium hydride, and barium hydride; at a temperature in the range of from about 20 C. to about 225 C.; under substantially anhydrous conditions;

and for a period of time suflicient to produce a polymer.

30. A process which comprises polymerizing a monomeric lactone admixture comprising two difierent alkylsubstituted epsilon-caprolactones with from about 0.01 to about 3.0 weight percent, based on the total Weight of the monomeric lactone feed, of a metal hydride selected from the group consisting of lithium hydride, potassium hydride, sodium hydride, rubidium hydride, cesium hydride, calcium hydride, strontium hydride, and barium hydride; at a temperature in the range of from about -20 C. to about 225 C.; under substantially anhydrous conditions; and for a period of time sufiicient to produce a polymer.

References Cited in the file of this patent UNITED STATES PATENTS 2,558,547 Eckey June 26, 1951 2,681,360 Vodonik June 15, 1954 2,809,958 Barnes et a1. Oct. 15, 1957 2,848,441 Reynolds et al Aug. 19, 1958 2,890,208 Young June 9, 1959 2,921,051 Amborski et a1 Jan. 12, 196.0

FOREIGN PATENTS 766,347 Great Britain Jan. 23, 1957 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,021,316 February 13, 1962 Eugene F. Cox et a1.

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 5, line 50, for "table," read table (hydrides of alkali metals), same column 5, in footnotefi, for "(1934)" read (1954) column 10, line 44, for v9o" read 90 c. columns 11 and 12, Table 1, line 1 of NOTE thereof, for -"n 32" read n3 same column 11, line 68,

"substitued" read substituted column 13, line 63, for

"60" read 5O column 14, lines 32 and 70 and 71, strike out "and aryloxy;", each occurrence, and insert instead aryloxy, a portion of an aromatic hydrocarbon nucleus which nucleus is fused to the cyclic ester ring, and a portion of a saturated nycloaliphatic hydrocarbon nucleus which nucleus contains from 4 to 10 carbon atoms and which is fused to the cyclic ester ring; column 14, line 41, and column 15, line 5, after "18,", each occurrence, insert and column 14, lines 44 to 51, and column 15, lines 7 to 14, strike out "four, (d) from 2 to 4 continuously linked carbon atoms contained in the cyclic ester ring can represent a portion of a saturated cyclocliphatic hydrocarbon nucleus which nucleus contains from 4 to 10 carbon atoms, and (e) the four R variables attached to any two adjacent Farbon atoms contained in the cyclic ester ring can represent a portion of a fused aromatic hydrocarbon nucleus;", each occurrence, and insert instead four; column 14, line 61, column 17, line 18, and column 18, line 3, strike out "different", each occurrence; column 15, lines 33, 58 and 73, column 16, lines 14, 29, 45 and 61, and column 17, line 14, strike out "a group IA metal hydride", each occurrence, and insert instead an alkali metal hydride Signed and sealed this 25th day of September 1962.

(SEAL) Attest:

ERNEST W. SWIDER DAVID L, LADD Attesting Officer Commissioner of Patents 

1. A PROCESS WHICH COMPRISES POLYMERIZING A CYCLIC ESTER CHARACTERIZED BY THE FOLLOWING FORMULA: 